Title of Invention

"AN IMPROVED DEVICE USEFUL FOR THE MEASUREMENT OF STRENGTH OF CONCRETE'

Abstract

An improved device useful for the measurement of strength of concrete which comprises a support (A) having a top plate (B) characterized in that the said top plate (B) provided with a concentric hole (C) at its top and an open bottom, a thrust bearing (D) being provided on the said concentric hole, the said support being provided with atleast one strain gauge (E) on its vertical surface, the output of the said strain gauge or gauges being measured by known means.

Full Text

This Invention relates to an improved device useful for the measurement of strength of concrete. The device of the present invention is useful for treating the strength and quality of the concrete of civil engineering structure either insitu or after the construction. In general the defect of the structures can be defined as the presence of some structural feature or physical or chemical property value, local or widespread, which prevents or night subsequently prevent a material or component in the structure from performing the desired functions. Some of such defects are Cracks, Corrosion, Porous voids, Unsuitable or low strength, which may result in structural failure. Non-Destructive Investigations : Non-Destructive Treating (NDT) is the science of diagnosing the presence or confirming the absence of defects in the objects such as engineering structures, components or materials, without the introduction of any change which degrade the intended purpose of the object. In industrial operations Non-Destructive Testing is part of the wider area of Quality control. The Non-Destructive Testing has been associated with the evaluation of the fitness of the object for a specific purpose rather than with the acquisition of new knowledge about a material. Non-Destructive Testing is considered essential for the safety of the aircraft, offshore oil installation, railroads, nuclear and conventional power stations, civil engineering structures etc. With the increasing emphasis on safety, quality control and product liability throughout industry, Non-Destructive Testing practice is becoming increasingly widespread beyond the confines of the traditional key users. Key User Industries : Civil Engineering construction: Concrete inspection, strength of concrete and its integrity. There are several methods and devices known to assess the quality of concrete and concrete structure methods/devices are used at two stages: 1. During the period of construction of the structure in order to assess the quality of the concrete/construction. 2. After construction to assess the damage fire or any other cause. The requirement in both the cases is to assess the strength of IN-SITU hardened concrete. The available methods based on the above requirements are following : 1. Rebound Hammer Test. 2. Ultrasound Pulse Velocity Test. 3. Penetration Resistance Techniques. 4. Pullout Test. REBOUND HAMMER TEST This test is non-destructive in nature as it does not require any drilling or penetration in the concrete. The test is based on simple theory of surface hardness. A mass having known energy is hit on the surface of the concrete the strength of which is to be tested and rebound of this mass is measured. This Rebound Hammer test was devised by Ernst Schmidt and is known as Schmidt Hammer test also. Rebound hammer test is conducted by using device shown in Fig, 1 of the drawing accompanying this specification. Different parts of the hammer are indicated by numbers in Fig. 1 and they represent to 1. Impact Plunger 3. Housing compl., 4. Rider with guide rod, 6.Pushbutton compl, 7. Hammer guide bar, 8. Disc, 9, Cap, 10. Two-part ring, 11. Rear cover, 12.Compression spring, 13.Pawl,14. Hammer mass, 15. Retaining spring, 16.Impact spring, 17. Guide sleeve, 18. Felt washer, 19. Plexiglass window scale printed on window, 20. Trip screw, 21. Lock nut,22. Pin, 23.Pawl spring. A spring loaded mass having a fixed amount of energy is impacted to it by extending a spring to a pin. This is achieved by pressing the plunger against the surface of the concrete to be tested. The release of the mass rebounds from the plunger which is still in contact with the concrete surface, and the distance traveled by the mass is measured, which is directly proportional to the strength of the concrete. The preparation of the surface of the concrete in this test method is extremely important. The large piece of aggregate in the area of the concrete is to be tested amount to the greater number of rebound numbers at the same time the presence of any void in the concrete may result in to a very less number of rebound numbers. Hence it is advisable to take about 10 reading in an area of 10cm x 10cm in such cases and their average value is taken. This rebound number is converted into strength of the concrete under test, using a calibration chart. ULTRASONIC PULSE VELOCITY TEST In most of the non-destructive methods it is difficult to take care of errors involved in investigations if the test are carried out on the sample taken and not on the actual structure of concrete. The best attempt could be to take out sample or core from the actual structure but the possibility of damage is always there. Attempts has been made to develop such a technique where the test may be carried out on the actual structure it self. An attempt in the same direction is the longitudinal wave velocity in the concrete has also been made. It has been observed that density and speed of such wave are closely related. The pulses of ultrasonic wave are generated by transducer and this transducer is placed on one side of the already prepared surface of the specimen of structure under test. The receiver of the equipment is placed on the another side of prepared surface of the same structure, and waves generated by transmitter are received in the receiver after traveling through the specimen. This sound energy is converted into an electrical energy and the transit time is measured and pulse velocity is calculated by dividing distance between transducers by the time. When access to two opposite sides is not available then pulse velocity can be measured on two perpendicular, or on the same surfaces of specimen as shown in Fig. 2(a) & 2(b) of the drawing accompanying this specification. Fig 2(a) depicts the direct method and Fig 2(b) shows the indirect method. The technique lacks precision where the ratio of mix is different as time duration for ultrasonic pulse depends on quality of concrete as well as voids in the concrete and the reasons can not be ascertained separately. Ultrasonic pulses velocity method can also be applied for the detection of cracks in the structures and preventive measures may be taken. PENETRATION RESISTANCE TEST Harder the concrete, it is more difficult to penetrate any object into it. This test is based on this principle and is commercially known as a Windsor Prove Test. Under Standard test conditions, the penetration is inversely proportion to the compressive strength of the concrete, but the relation depends upon the hardness of the aggregate. This test basically measures hardness and cannot yield absolute values of strength but is very useful in determining the relative strength. PULLOUT TEST Pullout Test is a very well known method of determining the strength of in-situ hardened concrete. In the conventional method some steel bolts/special nuts are put in concrete during the time of construction and they are pulled with the help of a pull out device using hydraulic jack or a torque wrench as and when required. The force required to pull out specific bolt is related to the strength of the concrete. The existing device is a conical shaped circular machined iron piece with a hole at the centre. It does not have any sensor to convert the compressive force into any other form of signal. It measures the pullout force with the help of hydraulic jack and pressure gauge. The load measuring device used with the existing device suffer from various defects, some of which are given as below:- Torque wrench has its own measurement limitations such as it is less accurate and needs adjustments during the test. In case of hydraulic jack and proving ring there are so many operating problems due to heavy weight such as decrease in oil pressure due to leakage leads to in-accuracy particularly in the field measurements where angular measurements are to be taken in structures. Turbine Building of power plant was damaged due to fire, and SERC Ghaziabad was requested to assess the extent of damage to the concrete without damaging the structure. Various available non-destructive test methods were considered for the assessment of insitu concrete of the structure. During our continued research on concrete structure the Non-destruct Test methods such as Rebound Hammer and Ultrasonic Pulse Velocity Test were conducted, but Pullout test was also considered essential to corroborate the results inorder to have a more reliable data. Under the available site specific conditions it was very difficult to use the available pull out devices as none of the known device were found suitable for the above work. This urgent requirement necessitated an attempt to develop a device which may work easily and accurately in such adverse field conditions. The main object of the present invention is to provide an improved device useful for the measurement of insitu concrete strength which can be easily operated and will provide accurate results. The schematic diagram of the various parts of the device of the present invention are shown in Fig 3 of the drawings. Fig 4 shows an embodiment of the complete device in actual use. Accordingly, the present invention provides an improved device useful for the measurement of strength of concrete which comprises a support (A) having a top plate (B) characterized in that the said top plate (B) provided with a concentric hole (C) at its top and an open bottom, a thrust bearing (D) being provided on the said concentric hole, the said support being provided with atleast one strain gauge (E) on its vertical surface, the output of the said strain gauge or gauges being measured by known means. The support used may be cylindrical or plurality of columns and the top plate may be integral or fixed to each other. The strain gauges used may be selected from electrical resistance strain gauge, semiconductor strain gauges and the like. The output of the strain gauges may be measured by known means such as full, half or quarter wheat stone bridge configuration Strain Indicators, Recorders, Instrumentation, Tape Recorders etc. and the like. The device of the present invention has been so constructed that pullout force is applied through an ordinary spanner. The pullout force gets converted into an electrical signal proportional to the load. Almost all the limitations have been eliminated and a new improved pullout test device has been invented. It can be used in all directions that is floor, wall, slabs and roof. The device is compact and is having less weight. The device of the present invention is explained with reference to figs. 3 & 4 of the drawings accompanying this specification. A round steel piece (B) with a concentric hole ( C ) is machined, hardened & grounded in the shape as indicated in Fig. 3 & 4 of the drawing . A heavy duty thrust bearing ( D ) & H.S.Washer ( I ) has been provided to minimize the frictional force. M.S.Bolt ( G ) full threaded is fabricated, and a nut is also provided in order to generate a pullout force. Electrical resistance wires gauges are pasted on the surface in order to form a quarter or half or a Full Bridge (Wheat Stone Bridge) Configuration. (H) is the concrete the strength of which being tested. (I) is epoxy or any other glue. The device is now ready for application. Round head bolts are fixed on the si .jojre' .nd Pullout Device is then attached with the bolt. The force is applied on nut with the help of a spanner, and a continuous out put in the form of electrical signal is available. This electrical output provides a variety of operating freedom, such as amplification and recording etc. The output signal is proportional to the applied force and the force required to take out the concrete cone is proportional to concrete strength. The following examples are given to illustrate the device of the present invention and these should not be construed to limit the scope of the invention . Example 1 Ten Nos. precast concrete cubes were taken and their strength was estimated with the help of available means that is rebound hammer and ultrasonic pulse velocity test. For pullout test the bolts were inserted in the cubes keeping the similar boundary conditions for all the cubes and enough time was given to cure the epoxy. All the bolts were then pulled out with the help of device and maximum strains acquired were noted with the help of a reliable strain indicator, for all the 10 cubes. It was notice that strength as determined by the rebound hammer and ultrasonic pulse velocity tests compares well with pull out tests. Two slabs (I M x I M ) have also been casted and similar tests have been carried out and the strength obtained has been compared by cubes tests. In order to calibrate the device a known load with the help of universal testing machine was applied on the device in intervals as indicated in fig. 5 and output in the form of strain was recorded. A graph, load Vs micro strains, was plotted, as indicated in fig.5. The graph so plotted revealed that strains measured can be directly translated in to load in terms of Kg/cm.sq. Example 2 The device was used on an actual building, plant whose TG foundation was damaged due to fire and this test was carried out on worst effected columns, beams and floor. The bolts were fixed at the desired locations, which were almost all the structural components i.e. wall, floor, roof. The bolts were then pulled with the help of device and strain reading were recorded for each individual bolt. The strength of concrete of each location was thus determined with the help of calibration chart, as shown at Fig.5. It was noticed that the strength determined with the help of device is matching with the strength determined through other known means. We claim : 1. An improved device useful for the measurement of strength of concrete which comprises a support (A) having a top plate (B) characterized in that the said top plate (B) provided with a concentric hole (C) at its top and an open bottom, a thrust bearing (D) being provided on the said concentric hole, the said support being provided with atleast one strain gauge (E) on its vertical surface, the output of the said strain gauge or gauges being measured by known means. 2. An improved device as claimed in claim 1 wherein the support is cylindrical or a plurality of columns. 3. An improved device as claimed in claims 1 & 2 wherein the top plate is integral or fixed to the support. 4. An improved device as claimed in claims 1-3 wherein the strain gauges used is selected from Electrical Resistance strain gauges, Semiconductor strain gauges, optical strain gauges. 5. An improved device as claimed in claim 1-4 wherein the output of the strain gauges is measured by known means such as quarter or full or half wheatstone bridge configuration, strain indicators, recorder instrumentation tape recorders . 6. An improved device useful for the measurement of strength of concrete substantially as herein described with reference to Figs. 3 to 4 of the drawings accompanying this specification and the examples.

Documents:

604-del-1995-abstract.pdf

604-del-1995-claims.pdf

604-del-1995-correspondence-others.pdf

604-del-1995-correspondence-po.pdf

604-del-1995-description (complete).pdf

604-del-1995-drawings.pdf

604-del-1995-form-1.pdf

604-del-1995-form-2.pdf

604-del-1995-form-4.pdf

604-del-1995-form-9.pdf